Host plant and the pathogens
Plantago lanceolata is a perennial wind pollinated rosette-forming herb (Sagar & Harper, 1964) with a worldwide distribution. In the Åland Islands, it occurs as a network consisting of ca. 4000 meadows in a highly fragmented landscape (Ojanen et al., 2013). Annually in September, the 4000 P. lanceolata populations’ size, area, and location are monitored and the presence of Podosphaera plantaginis fungus and Melitaea cinxia butterfly are surveyed. (Jousimo et al., 2014, Ojanen et al., 2013). In Åland P. lanceolata has been discovered to host two fungal pathogens (Laine, 2003, Jousimo et al., 2014) and five viruses (Susi et al., 2019) thus far. Phomopsis subordinaria (telemorph Diaporthe adunca(Rob.) Niessl.) is a specialist fungal pathogen of P. lanceolata(Laine, 2003) transmitted by weevil Trichosirocalus troglodytes(de Nooji & van der Aa, 1987, Nieminen & Vikberg, 2015). The pathogen infects its host plant through a wound under the inflorescence of the plant causing the developing seeds to dry out (de Nooji & van der Aa, 1987). The pathogen kills the plant cells and feeds on dead tissue, subsequently causing death of the whole plant. It produces pycnidia in which its spores are formed. Here, we use pycnidia formation as a measure of transmission potential of the pathogen. Plantago lanceolata latent virus (PlLV) is a DNA virus belonging to Capulaviruses in Geminiviridae (Susi et al., 2017). The virus has been recently characterized (Susi et al., 2019, Susi et al., 2017) , and it is relatively common in populations of P. lanceolata in the Åland Islands (33% of populations infected)(Sallinen et al., 2020). Mode of transmission and potential host range of PILV are currently unknown.